Objectives: 1. Analysis of the functional constituents of the peptidoglycan crosslinking enzyme system responsible for the synthesis of a round and fragile wall peptidoglycan layer by the unstable L-form of Proteus mirabilis in the presence of high concentrations of penicillin. 2. Resolution, characterization and isolation of the essential constituents of the peptidoglycan crosslinking enzyme system in Streptococcus faecalis and Streptomyces sp. 3. Use of model enzymes in determination of the mechanism of action of pencillins and delta 3-cephalosporins at the molecular level and of the effects that the structural features of the antibiotic molecule exert on the various steps which govern the reaction between the enzymes and the antibiotics.